Calcium oscillations exert physiological control on mitochondrial energy metabolism but can also induce mitochondrial membrane permeabilization and ensuing cell death. The specificity of the mitochondrial calcium signaling is dependent on the coincident presence of stress factors like ceramide, reactive oxygen species (ROS) and on the amount and spatiotemporal pattern of the Ca2+ load to the mitochondria. The latter factor is coming into focus based on recent evidence revealing that many human cardiac/skeletal muscle and neurodegenerative diseases are associated with mutations of the intracellular Ca2+ release channels and their regulatory proteins and present early mitochondrial impairments. However, the dependence of the mitochondrial injury on the altered Ca2+ mobilization remains elusive. Our hypothesis is that sensitization of IP3R/RyR-mediated Ca2+ release may cause a shift from the physiological to the pathophysiological range of mitochondrial calcium signaling and that a variety of mutations associated with human skeletal (malignant hyperthermia) and cardiac muscle (Idiopathic paroxysmal ventricular tachycardia) and neurodegenerative diseases (e.g. Huntington disease) may evoke mitochondrial derangements and cell injury by this mechanism (Aim#1). Furthermore, we suggest that the Ca2+ transfer across the outer mitochondrial membrane (Aim#2), the matrix Ca2+ buffering by cardiolipin (Aim#3) and the distribution of mitochondria relative to the source of the [Ca2+] rise (Aim#4) are important factors in determining the potency of Ca2+ to trigger cell death. The research plan integrates genetics, advanced imaging and biochemistry approaches to unravel mechanisms, regulation and consequences of mitochondrial membrane permeabilization driven by calcium signals. We have developed an array of live cell imaging approaches to visualize and quantitate ER/SR- mitochondrial calcium handling. The studies will focus on the injury of cardiac/skeletal muscle, and brain, where cell function relies on a high capacity of mitochondrial metabolism that can be regulated on demand. The experiments are organized into four aims as follows: (1) To test the hypothesis that mutations promoting Ca2+ release through IP3R and RyR may elicit mitochondrial Ca2+ overload and make mitochondria vulnerable to membrane permeabilization. (2) To test the idea that expression of distinct VDAC isoforms differentially regulate the mitochondrial Ca2+ transport and the Ca2+-induced and tBid-induced membrane permeabilization, (3) To test the dependence of mitochondrial calcium signaling and calcium-induced apoptosis on cardiolipin (4) To test the hypothesis that the Ca2+ oscillation-induced mitochondrial injury and cell death is dependent on the spatial distribution and motility of the mitochondria. Understanding the pathophysiological mechanisms of ER/SR-mitochondrial Ca2+ handling will afford insights into the pathogenesis of human diseases and ma open new avenues for developing diagnostic, prognostic and therapeutic tools. PUBLIC HEALTH RELEVANCE: Genetic defects of intracellular calcium release channels cause enhanced calcium mobilization in multiple tissues. Mitochondria are a key target of the calcium's effect, which underlies changes in mitochondrial function and morphology which, in turn, lead to mitochondrial dysfunction. Recent progress in the study of mitochondrial structure and function in live cells will enable us to establish the mechanisms, regulation and significance of mitochondrial calcium signaling and permeabilization in cell injury caused by genetic defects and by environmental factors in calcium release or in mitochondrial calcium sensing.